This invention relates to copolymer materials which are useful as ophthalmic devices, such as contact lenses, intraocular lenses (IOLs), keratoprostheses, and corneal rings or inlays, and a process for making and using such copolymer materials. In particular, this invention relates to intraocular foldable lenses formed from acrylic copolymer materials.
With recent advances in small-incision cataract surgery, increased emphasis has been placed on developing soft, foldable materials suitable for use in artificial ophthalmic lenses. In general, these materials fall into one of three categories: hydrogels, silicones, and generally, others.
The refractive power of a lens is a function of its shape and the refractive index of the material of which it is made. A lens made from a material having a higher refractive index can be thinner and provide the same refractive power as a lens made from a material having a relatively lower refractive index. Thinner lenses are easier to insert and cause less trauma during surgery.
Hydrogel materials are hard or rigid when dry, and absorb a large amount of water (e.g., up to 20-70% by weight) when hydrated, which lowers the refractive index of the material. These materials tend to be brittle when dry, and have poor mechanical properties for ophthalmic applications. In a hydrated state, hydrogel materials become soft and pliable. Known hydrated hydrogels have a relatively low refractive index, for example, less than 1.48. In addition to adversely affecting the refractive index, the absorbed water also significantly increases the diameter and thickness of the IOLs, for example, by as much as about 15 percent.
Silicone materials have a slightly higher refractive index (for example, 1.51), but tend to unfold too rapidly after being placed in the eye in a folded configuration. The biocompatibility of silicone materials may also be a concern.
U.S. Pat. No. 5,290,892 (Namdaran et al.), U.S. Pat. No. 5,331,073 (Weinschenk, III et al.), and U.S. Pat. No. 5,693,095 (Freeman et al.), the complete disclosures of which are hereby incorporated by reference, discuss forming foldable lenses out of a polymer material derived from an ethoxyaryl (meth)acrylate with a crosslinker or with a second acrylate monomer and crosslinker. Since the polymer material is soft/foldable, those patents discuss mold forming the polymer material to individually form the lens. Likewise, U.S. Pat. No. 5,433,746 to Namdaran et al., which is herein fully incorporated by reference, discloses forming flexible intraocular lenses by molding polymeric materials which have a relatively low glass transition temperature. Such molding requires specialized equipment and expensive customized molds. In addition, the resulting molded lenses tend to have poor surface quality since they generally cannot be polished. Alternatively, U.S. Pat. No. 5,331,073 discusses forming lenses from a soft/foldable material by machining the lenses at cryogenic temperatures. Such a process is cumbersome and expensive.
A foldable, high refractive index material, which may be machined and polished using conventional technology, would be a significant advancement in the art.